Method and system for controlling the driving stability of a vehicle and use of said system

ABSTRACT

The present device relates to a system and method for controlling the driving stability of a vehicle utilizing variables that characterize a driving situation of the vehicle and are detected in a process. The system and method include determining an expected future behavior of the vehicle, checking the expected future driving behavior with respect to a critical driving situation and executing a vehicle intervention during stable driving conditions to prevent the vehicle from entering a critical driving situation. The intervention may include a brake intervention or an engine intervention.

BACKGROUND OF THE INVENTION

The present invention relates to a method for controlling the drivingstability of a vehicle wherein variables characterizing a drivingsituation of the vehicle are detected in a process.

The invention further relates to a system appropriate for implementingthe method and to the use of the system.

Prior-art driving dynamics control systems detect the vehicle behaviorby means of appropriate sensors and compare the vehicle behavior, whichis influenced by the driver among others by way of the steering system,with the reference behavior for the vehicle. Discrepancies between thevehicle behavior and the reference behavior are controlled by brakeinterventions and engine interventions.

Among these systems are above all embodiments of brake slip control(ABS) meant to prevent individual wheels from locking during a brakeoperation, traction slip control (TCS) meant to preclude spinning of thedrive wheels, the electronic brake force boosting (EBV) for controllingthe ratio between the brake force at the front axle and at the rearaxle, anti rollover braking (ARB) for preventing rollover of the vehicleabout its longitudinal axis, and yaw torque control (ESP) forstabilizing the vehicle in a yawing motion.

However, the above control systems react only when a deviation of thevehicle behavior from the reference behavior has already been detected.Thus, they are only in a position to improve the vehicle behavior in acritical driving situation, yet they are unable to prevent criticaldriving situations.

In particular when the driver provokes a critical driving situation byadjusting safety-critical steering angle velocities or steering angles,respectively, it is initially necessary for the control systems todetect the reaction of the vehicle before they can intervene intodriving dynamics. Thus, the driver can force a vehicle intosafety-critical situations which may cause skidding or rollover.

In this regard, U.S. National Highway Traffic Safety Administration(NHTSA) planned to perform a test with respect to the RolloverResistance in order to check a vehicle in the described situation. FIG.1 illustrates the high demands placed on the vehicles in this test.

It is desirable that driving dynamics control systems can reliablydetect and prevent any possible critical driving situations at an earlytime. Some systems for the early detection of driving situations with asafety hazard are known in the art.

Thus, international patent application WO 02/36401 A1 discloses a methodfor controlling the driving stability, wherein it is determined on thebasis of a stable driving behavior whether there is a tendency to asubsequent unstable driving behavior due to a highly dynamic steeringmaneuver, and pre-intervention of the brake will take place already at astable driving behavior in this case. Based on the comparison of thesensed steering wheel angle velocity, the yaw rate, and/or the lateralacceleration with predetermined threshold values it is judged whetherthe vehicle shows a tendency to unstable driving behavior.

This prior art method differs from the methods which are the basis forthe systems reacting to a critical situation in that said method becomesactive already when the vehicle is still showing a stable behavior.However, like the prior art reactive methods, it founds on thecomparison of actual data with threshold values that lead to expect anunstable driving behavior. These values must be determined from tests bymeans of a reference model of the vehicle, with the problem beingencountered that individual driving situations, which are e.g.determined by the instantaneously prevailing load of the vehicle and thecondition of the underground, cannot be taken into accountcomprehensively, or only by entailing considerable efforts.

SUMMARY OF THE INVENTION

Starting from the illustrated state of the art, an object of theinvention is to improve upon a generic method and a generic system insuch a fashion that driving situations with a safety hazard are morereliably detected at an early time and prevented more effectively.

According to the invention, this object is achieved by a method thatdetermines driver actions, determines expected future driving behaviorof the vehicle, checks if the behavior will be a critical drivingsituation and executes an intervention while the vehicle is in a stabledriving condition.

Further, the object is achieved by a system that determines driveractions, determines expected future driving behavior of the vehicle,checks if the behavior will be a critical driving situation and executesan intervention while the vehicle is in a stable driving condition.

According to the invention, a method is implemented for controlling thedriving stability of a vehicle, wherein variables characterizing thedriving behavior of a vehicle are detected in a process, a driver actionis determined from the detected variables, a driving situation to beexpected in future due to the driver action is defined and this drivingsituation is checked with respect to whether the driving situation iscritical. If the driving situation to be expected is assessed as beingcritical, brake interventions and/or engine interventions are executedalready when a stable driving behavior prevails, said interventionschanging the driving situation in such a fashion that the drivingsituation that has to be expected in view of the driver action will notoccur.

Thus, the method involves that the driving behavior is monitored and thedriving situation to be expected in future is evaluated in order todetect critical driving situations at an early time. Hence, theinvention goes beyond testing the instantaneous driving situation whichserves as an indicator of future driving behavior in the prior artmethod. The prediction of the driving behavior to be expected, accordingto the invention, is based on the detected driver action and is, thus,more reliable and better adapted to situations than a calculation of thefuture vehicle behavior from the actual data of driving dynamics andlimit values linked thereto which are determined in a vehicle model witha skilled driver.

A typical driver action which can lead to a safety-critical drivingsituation is e.g. a steering movement with a very great steering wheelangle gradient. The method of the invention allows determining from thedriving-dynamics relevant variables, which are measured when thissteering movement is initiated, the values of these variables to beexpected, and allows comparing them with predeterminedsituation-responsive limit values. When the limit values are exceeded,corresponding brake and/or engine interventions can be performed toavoid the occurrence of a critical driving situation.

Another advantage of the method of the invention is that it can beintegrated into the implementation of an electronic driving stabilityprogram.

It is therefore especially favorable that the process in which therelevant variables are measured concerns a driving stability program forvehicles.

In a preferred embodiment of the method, at least the process variablessteering wheel angle and/or steering angle and vehicle speed aremeasured, and the term ‘vehicle speed’ implies the speed of the centerof gravity of the vehicle.

An early, critical vehicle situation can e.g. be determined in that thedriver action is determined by means of an instantaneous lateralacceleration a_(y1) that is produced from the process variables‘steering angle’ and ‘vehicle speed’ by taking into account vehicleconstants.

It is favorable to this end that the lateral acceleration a_(y1) isdetermined which the vehicle would reach if the driver continued drivingwith the currently adjusted steering angle.

An early critical vehicle situation can be determined in a particularlypreferred embodiment of the method in that the driver action isdetermined by means of a lateral acceleration a_(y2) which is producedfrom the process variables ‘steering angle speed’ and ‘vehicle speed’and has to be expected in future.

It is favorable in this arrangement that the lateral acceleration a_(y2)to be expected in future is determined, which the vehicle would reach ifthe driver continued driving into or out of a bend with almost the samesteering velocity.

When determining the critical vehicle situation, it is furthermoreadvantageous that the determined variables of the lateral accelerationsa_(y1), a_(y2) are compensated with respectively one or at least onelimit value.

A critical vehicle situation is favorably eliminated because the brakeinterventions are carried out on at least one wheel.

Furthermore, a critical driving situation is favorably eliminatedbecause the vehicle speed is reduced by the brake interventions.

The yaw rate of the vehicle is another example of a driving-dynamicsrelevant variable which can be monitored by means of the method of theinvention.

A critical driving situation can be detected in that actual rotationdata measured by means of a yaw rate sensor and/or yaw angle sensor arecompared with nominal rotation data. As this occurs, it is favorablethat the nominal rotation data are determined from the process variablesin a vehicle model.

It is preferred that a yaw rate to be expected in future is determinedbased on the measured actual yaw rate data. The yaw rate to be expectedcan be compared with nominal rotation data in order to detect a drivingsituation with a safety hazard due to a driver action at an early time.

If any one of the comparisons leads to expect a critical drivingsituation, it is possible that the brake interventions, depending onactual and nominal rotation data, force an additional torque about thevertical axis of the vehicle, meaning a yaw torque which compensates thedriver action.

It is then arranged for that signals for a pressure requirement aimingat a brake pressure increase and/or brake pressure reduction in thewheel brakes are generated in a driving dynamics control, which pressurerequirement causes a determined additional torque or a determined speedreduction of the vehicle, and the corresponding commands are output tothe actuators.

The intensity of the brake intervention is favorably determined in thatthe signals for the brake pressure increase and/or brake pressurereduction are produced depending on the variables of the lateralaccelerations a_(y1), a_(y2) and/or the vehicle speed and/or the actuallateral acceleration and/or the steering wheel angle.

It is favorably provided that the brake and/or engine torqueintervention is terminated when the expected critical driving situationfails to appear or an actual critical driving situation is no longerdetermined.

A condition for leaving the control is that the critical drivingsituation is no longer determined when the variables of the lateralaccelerations a_(y1) and a_(y2) are below predetermined thresholdvalues.

Besides, the invention offers a system which is appropriate forimplementing the method of the invention. The term ‘system’ hereinespecially implies a device in which the components cooperate.

The system for controlling the driving stability of a vehicle comprisessensors, which characterize the driving behavior of the vehicle andmeasure variables taken into account in a process, a unit for evaluatingthe measured values of the variables, and a means for generating controlsignals for controlling a brake and/or engine intervention.

The system further comprises a means for determining a driver actionfrom the values of the variables measured during a process, a means fordetermining values of variables that characterize a driving dynamics ofthe vehicle and can be derived from the measured variables and vehicleconstants, said values to be expected in future due to the determineddriver action, a means of comparison for comparing the values of thesevariables to be expected with threshold values for these variables andfor checking whether a critical driving situation must be expected, andin addition comprises a means for controlling brake and/or engineinterventions depending on the result of the comparison.

When the result of the comparison is that a critical driving situationhas to be expected, this situation can be prevented by appropriate brakeand/or engine interventions.

In a preferred embodiment, the system comprises at least one sensor fordetecting the vehicle speed and a sensor for detecting the steeringangle and/or the steering wheel angle.

It is also very favorable that the system also comprises a sensor fordetecting the yaw rate of the vehicle.

Another advantage of the system involves that it can be integrated intoa driving stability control such as ABS, TCS, ESP and a similar system.

The system is further suited in a very favorable way for use in a devicefor preventing rollover of a vehicle.

Further advantageous ways of implementing the method of the inventionand further favorable embodiments of the system of the invention can betaken from the following illustration of preferred embodiments of theinvention by way of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an illustration of the test conditions of the NHTSA test fordetermining the Rollover Resistance Rate;

FIG. 2 is a schematic view of a vehicle with a brake control system.

DETAILED DESCRIPTION OF THE DRAWINGS

Each vehicle has, likewise at a high coefficient of friction, a maximumlateral acceleration which depends on the roadway-tire material pairing,on the chassis and, eventually, on the center of gravity of the vehicle.Tests have shown that unskilled drivers will mostly steer too late andoften excessively in dangerous situations, thus exceeding the physicallimits of the vehicle.

It is preferred to use the system in a driving dynamics control systemsuch as ABS, TCS, ESP, etc., or in a device for rollover prevention ofvehicles. Vehicles being equipped with these systems are alreadyprovided with the necessary sensor equipment and include the requiredactuators.

The method of the invention and the system of the invention are used toavoid vehicle instabilities which may occur due to abrupt steering andcountersteering reactions as possibly encountered in an obstacleavoidance maneuver, during lane changes, and like maneuvers. Inparticular in vehicles with a high center of gravity there is a majorrisk of rollover in these maneuvers.

The driving situations referred to hereinabove are e.g. provoked in thetests planned by the U.S. NHTSA in order to determine the RolloverResistance of vehicles. The envisaged maneuvers are illustrated in FIG.1.

Initially, the steering wheel turn and, hence, the steering wheel angleγ is increased slowly at a constant vehicle speed of v=80 km/h until thecentrifugal acceleration at the vehicle's center of gravity amounts to0.3 g. With the corresponding steering wheel turn, the steering wheelangle γ is determined which corresponds to this turn.

The actual test comprises a ‘J-turn’ and a ‘fishhook’ maneuver.

In the ‘J-turn’ maneuver, the steering wheel angle γ is raised with asteering angle gradient γ from 1000°/s to a value of 8 γ.

The ‘fishhook’ maneuver is characterized in that the steering wheelangle γ initially at a steering wheel angle gradient γ of 720°/s israised to an angle γ of 6.5 γ° and is then maintained constant until attime τ the maximum roll angle is reached, that means the maximumdeflection of the vehicle with respect to a rotation about itslongitudinal axis. Subsequently, the steering wheel is turned back untila steering wheel angle γ of −6.5 γ° is reached. The change of thesteering wheel angle γ when steering back to the original course shallcorrespond also to a steering wheel angle gradient γ of 720°/s.

Positive or negative steering wheel angles γ correspond to right-hand orleft-hand curves, or vice-versa. It is not important which directioncorresponds to which sign.

Thus, very great steering angles γ and very high steering anglegradients δ appear in the described maneuvers. Overturning or rolloverof the vehicle may occur especially in an obstacle avoidance maneuverwith countersteering at a high coefficient of friction that is simulatedby the ‘fishhook’ maneuver.

In general, two driver actions have been found in the preparation of theinvention which, occurring individually and jointly, must be assessed ascritical.

They cause a swerving hazard and, at high coefficients of friction, mayeven cause overturning or rollover of the vehicle, respectively.

The actions concerned are

-   a) steering with a very high gradient, and-   b) ‘oversteering’, meaning that the driver adjusts a steering angle    δ which significantly exceeds the physical possibilities of the    vehicle.

Likewise the NHTSA test described hereinabove founds on a considerationof these critical driver actions. In particular in vehicles which, withrespect to their track width, have a very high center of gravity, thesedriver actions can cause an uncontrolled turning into a bend androllover in the worst case. Among the vehicle species with a specialsafety hazard are e.g. LTV (Light Trucks and Vans) and SUV SportsUtility Vehicles) vehicles.

The invention at issue provides a method and a system, which reliablyand early detect such driver actions and avoid safety-criticalsituations by appropriate brake and/or engine interventions.

To this effect, the invention makes use of the system comprising sensorsand actuators which is are typically provided in vehicles with an ESPsystem. The ESP sensor equipment and the brake control system of avehicle of this type are shown schematically in FIG. 2.

The ESP system comprises a wheel speed sensor 1 for each of the fourwheels of the vehicle, a tandem master cylinder (TMC) pressure sensor 2,a lateral acceleration sensor 3 for determining the lateral accelerationa_(y), a yaw rate sensor 4 for detecting the yaw rate {dot over (Ψ)} anda steering wheel angle sensor 5 for detecting the steering wheel angleγ.

The test signals of the sensors are transmitted to the vehicle processorsystem (ECU) 8, as is indicated by the dotted lines in FIG. 2.

It is assumed in this embodiment that the vehicle is equipped with ahydraulic brake. The use of an electro-hydraulic or electromechanicalbrake is, however, also possible.

In a hydraulic brake system, the brake pressure is built up by thedriver by way of the brake pedal actuating a master brake cylinder(TMC), and the brakes 6 at the individual wheels are connected to themaster cylinder (TMC) by way of inlet valves. Outlet valves, throughwhich the wheel brakes 6 are in connection to a non-pressurizedreservoir or a low-pressure accumulator, control a reduction of thebrake pressure. The inlet and outlet valves are electromagneticallyoperated for pressure control.

In addition, an auxiliary pressure source is provided that is used tobuild up brake pressure in the wheel brakes 6 independently of theposition of the brake pedal.

The brake pressure in the master cylinder (TMC) is adjusted byapplication of the brake pedal so that the TMC pressure sensor can bereplaced by a pedal-travel or pedal-force sensor in order to sense thebraking request of a driver. A TMC pressure can then be associated withthe test signals in each case.

Similarly, a steering angle sensor can replace the steering wheel anglesensor 5 because there is a predefined relationship between the steeringangle δ of the front wheels and the steering wheel angle γ.

The master cylinder (TMC) of the hydraulic brake system his connected byway of hydraulic lines to a hydraulic unit (HCU) 7 for actuating thebrakes 6. The hydraulic unit (HCU) 7 receives control signals from thevehicle processor system (ECU) 8 and permits an individual actuation ofthe single wheel brakes 6, as it is executed by an ESP.

The interaction of the individual components of the brake system takesplace by way of hydraulic lines which are schematically shown in FIG. 2by solid lines.

The first approach of the invention relates to the detection of thephysical lateral acceleration limit and the cornering force which thedriver demands from the vehicle.

It is then determined whether a steering request of the driver comprisesa steering angle δ or a steering angle gradient δ, respectively, whichis of such a magnitude that the lateral acceleration a_(y) that has tobe expected due to the steering request exceeds a predeterminedthreshold value.

The lateral acceleration a_(y) to be expected due to the steeringrequest is determined in the fashion that will be described hereinbelow:

Between the vehicle speed v, the lateral acceleration a_(y) and the yawrate {dot over (Ψ)} there is, on the one hand, the relation{dot over (Ψ)}·ν=α_(y)   (I)where the variables are related to the center of gravity of the vehicle.On the other hand, $\begin{matrix}{\overset{.}{\Psi} = \frac{\delta \cdot v}{l + {{v^{2} \cdot E}\quad G}}} & ({II})\end{matrix}$also applies to the yaw rate {dot over (Ψ)}, this term also implying adependency of the yaw rate {dot over (Ψ)} on the steering angle δ andthe so-called self-steering gradient EG. The self-steering gradient EGof the vehicle indicates the self-steering behavior of the vehicle, thatmeans the steering properties at the lateral acceleration a_(y)independent of a driver's influence. Depending on whether theself-steering gradient EG is higher than zero, equal to zero, or lowerthan zero, the vehicle behaves in an oversteering, neutral, orundersteering fashion. This results from the fact that the variableEGa_(y) indicates exactly the difference of the tire slip angles on thefront and rear axles. Reference numeral 1 designates the wheel base ofthe vehicle.

The terms (I) and (II) for the yaw rate {dot over (Ψ)} can be equatedand solved with respect to a_(y) in order to achieve a term for thelateral acceleration a_(y) depending on the vehicle speed v, the sensedsteering angle δ and the vehicle-responsive parameters of wheel base 1and self-steering gradient EG: $\begin{matrix}{a_{y\quad 1} = {\frac{\delta \cdot v^{2}}{l + {{v^{2} \cdot E}\quad G}}.}} & ({III})\end{matrix}$

This term indicates the instantaneous lateral acceleration a_(y1) of thevehicle in particular in dependence on the instantaneous (measured)steering angle δ. The variable a_(y1) thus corresponds to the lateralacceleration, at which the vehicle would theoretically ride in aconstant circular travel with the currently adjusted steering angle δ.

The instantaneous lateral acceleration a_(y1) can also be measured bymeans of the lateral acceleration sensor 1.

When the value of a_(y1) exceeds a defined, situation-responsive limitvalue (e.g. 9-11 m/s²), it can be assumed that the steering angle of thedriver is excessive for the current speed v. This means a criticaldriving situation exists which can cause unstable driving behavior and,at a high coefficient of friction, also rollover of the vehicle.

However, the term (III) in this form still does not allow the forecastaccording to the invention regarding the lateral acceleration a_(y) thathas to be expected and desired or provoked by the driver by way of itssteering behavior, when the driver continues changing the steering angleδ.

However, a behavior of this special type is frequently observed inunforeseen obstacle avoidance maneuvers.

The difference between the steering angle δ against time t and theinstantaneous steering angle, however, results under the precondition ofa constant steering angle gradient {dot over (δ)} to {dot over (δ)}t.The invention aims at predicting the lateral acceleration for a shorttime t after the measurement of the lateral acceleration a_(y) or of thevariables determining the latter.

The time during which the forecast shall be directed into the future isreferred to as LcPaytime and amounts up to 1 s. A typical value whichtakes into account the steering performance of the driver and theresponse behavior of the electronic and the brake systems and thevehicle amounts to 300 ms.

The lateral acceleration a_(y2) to be expected on account of the driveraction is thus achieved by the term $\begin{matrix}{a_{y\quad 2} = {\frac{\left( {\delta + {\overset{.}{\delta} \cdot {LcPaytime}}} \right) \cdot v^{2}}{l + {{v^{2} \cdot E}\quad G}}.}} & ({IV})\end{matrix}$The lateral acceleration a_(y2) comprises the theoretical lateralacceleration a_(y), which the vehicle would have in the future (in thetime LcPaytime) if the driver continues driving into or out of a bendwith a uniform steering velocity δ.

The steering angle gradient {dot over (δ)} can be determined from twovalues of the steering wheel angle γ being measured in short successionor of the steering angle δ.

When the signal a_(y2) exceeds a defined, situation-responsive limitvalue (e.g. 6-15 m/s²), it can be assumed that the steering angle of thedriver within a short period will be too great for the current speed.This means it must be assumed that a critical driving situation willsoon prevail that may lead to unstable driving behavior and, at a highcoefficient of friction, can even cause rollover of the vehicle.

Thus, the signals a_(y1) and a_(y2) allow a reliable and, in particularby way of the signal a_(y2), early detection of a driver action whichcan lead to a critical driving behavior. In order to prevent theoccurrence of critical driving situations, the brake control system isactivated which can reduce the vehicle speed by means of brakeintervention and/or force the vehicle into an understeering maneuver dueto an asymmetric brake intervention. The pressure increases can then gobeyond the wheel lock pressure level in order to purposefully reduce thecornering force at the wheels undergoing intervention.

The situation-responsive limit values are determined at a referencevehicle and stored in the vehicle processor system (ECU).

The vehicle processor system (ECU) comprises a means for determining thelateral accelerations a_(y1) and a_(y2) from the data transmitted by thesensor equipment of the overall system.

The instantaneous lateral acceleration a_(y1) can be calculatedaccording to the term (III) by the means for determining the lateralacceleration or can result directly from the test signal of the lateralacceleration sensor 3.

To calculate the instantaneous lateral acceleration, the means receivesthe test signals of the steering wheel angle sensor 5 and the signals ofthe wheel speed sensors 1 from which the vehicle speed v can bedetermined.

The vehicle constants such as wheel base 1 and self-steering gradient EGare stored in the vehicle processor system (ECU) 8.

The redundant measurement also allows checking the function of thesensors by means of the vehicle processor system (ECU) 8. Thus, thecomparison of the calculated value of a_(y1) with the test signal allowschecking the test signal of the steering angle sensor 5.

The system further has a comparison means comparing the values for thelateral accelerations a_(y1) and a_(y2) that have been determined by wayof the test data transmitted from sensors, with the stored limit values.In dependence on the result of the comparison, the vehicle processorsystem (ECU) generates corrective signals, which are transmitted to thehydraulic unit (HCU) 7 and initiate a brake intervention. Thetransmission of the corrective signals is shown schematically in FIG. 2by means of an arrow.

The limit values are responsive to the situation in a preferredembodiment of the invention. In case there is corresponding sensorequipment, they can take into consideration the weather, road pavements,and possibly further parameters.

The intensity of the brake intervention can then be dependent on thesignals a_(y1) and a_(y2) and on the driving speed v, the actual lateralacceleration a_(y1), the steering angle δ.

All variables or the corresponding test signals, respectively, areprocessed by the vehicle processor system (ECU) 8, which subsequentlygenerates corresponding control signals and sends them to the hydraulicunit (HCU) 7. This unit will then actuate the wheel brakes 6 in responseto the control signals.

As this occurs, brake intervention is preferably executed either at thefront wheels or at the outside front wheel in a turn. In particular ifintensive brake intervention becomes necessary, it is preferred to slowdown both front wheels because braking of the outside wheel in a turnalone could generate an excessive yaw torque so that the vehicle mightbe skidding.

However, in less intensive brake interventions it is preferred to brakethe outside wheel in a turn in order to force the vehicle into anundersteering maneuver. This can further be achieved in that a wheel isbraked to such a great extent that it locks for a short interval. Thiscauses a reduction of cornering force and can also bring aboutundersteering of the vehicle. Thus, the brake system is controlledanalogously to the control by way of an ESP system.

In a favorable embodiment, the system of the invention in additioncomprises a means for engine intervention. This means permits brakingthe vehicle by means of reducing the engine torque in order to avoidsafety-critical driving situations. In this arrangement, engineintervention can be executed in addition to brake intervention.

Furthermore, it is especially favorable when the yaw rate {dot over (Ψ)}determined from the test signals of the yaw rate sensor 4 is taken intoconsideration in the control of the brake and/or engine interventions.

This factor allows controlling the brake and/or engine interventions insuch a fashion that an additional yaw torque is forced which counteractsa safety-critical yaw motion.

Also, arrangements may be made in this respect to determine in additionto the instantaneous yaw rate {dot over (Ψ)} also that yaw rate {dotover (Ψ)}₁ which would occur if the driver continued driving into or outof a bend at a uniform steering velocity {dot over (δ)}.

Analogously to the relation (IV), the yaw rate {dot over (Ψ)}₁ isachieved from the term (II) with $\begin{matrix}{{\overset{.}{\Psi}}_{1} = {\frac{\left( {\delta + {\overset{.}{\delta} \cdot {LcPaytime}}} \right) \cdot v}{l + {{v^{2} \cdot E}\quad G}}.}} & (V)\end{matrix}$The expected yaw rate determined therefrom can be compared with amaximum yaw rate determined by way of a reference model of thecorresponding vehicle, the maximum yaw rate ensuring a safe drivingsituation. When the value of the yaw rate to be expected exceeds thismaximum yaw rate, the vehicle processor system can initiate a correctingbrake and/or engine intervention at an early time.

The brake intervention and/or engine intervention can be terminated assoon as the critical driving situation is overcome and/or the values ofa_(y2) and Ψ₁ or {dot over (Ψ)}₁ can lead to expect a safe drivingsituation.

This condition can e.g. be detected when the signals a_(y1) and a_(y2)fall short of determined limit values (e.g. 5-10 m/s²).

Thus, the invention provides a favorable method and a system allowingearly detection of driving situations with a safety hazard and, hence,avoiding their occurrence.

Thus, the invention goes beyond making available a reactive system thatintervenes in the event of existing vehicle instability (e.g. deviationof the measured yaw rate {dot over (Ψ)} from the nominal yaw rate,exceeding of the lateral acceleration threshold). The invention rathercomprises a system that is foresightedly activated in expectation offuture instability.

As this occurs, the driver action plays the predominant role, and anenormous advantage in time is achieved because there is no need to waitfor vehicle reactions.

LIST OF REFERENCE NUMERALS

-   1 wheel speed sensor-   2 tandem master cylinder (TMC)—pressure sensor-   3 lateral acceleration sensor-   4 yaw rate sensor-   5 steering wheel angle sensor-   6 wheel brake-   7 hydraulic unit-   8 vehicle processor system-   ECU vehicle processor system-   HCU hydraulic unit-   THZ tandem master cylinder-   a_(y) lateral acceleration-   a_(y1) instantaneous lateral acceleration-   a_(y2) lateral acceleration to be expected-   δ steering angle-   {dot over (δ)} steering wheel angle gradient-   EG self-steering gradient-   γ steering wheel angle-   {dot over (γ)} steering wheel angle gradient-   γ* steering wheel angle at 0.3 g-   l wheel base-   {dot over (Ψ)} yaw rate-   {dot over (Ψ)}₁ yaw rate to be expected-   t time-   τ time at which the vehicle has reached its maximum roll angle-   v vehicle speed

1-25. (canceled)
 26. A method for controlling driving stability of avehicle using variables that characterize a driving situation of thevehicle, the method comprising: determining driver actions from detectedvariables; determining an expected future driving behavior of thevehicle based on the determined driver actions; checking the expectedfuture driving behavior with respect to a critical driving situation;and executing at least brake interventions or engine interventionsduring stable driving behavior when a critical driving situation isexpected in the future.
 27. The method according to claim 26, whereinthe variables are determined by an electronic driving stability programprocess.
 28. The method according to claim 26, wherein the variablesinclude at least one of a vehicle speed, a steering wheel angle and asteering angle.
 29. The method according to claim 28 further comprising:determining a first lateral acceleration the vehicle is expected toreach when the driver continues driving with the current steering wheelangle.
 30. The method according to claim 29 further comprising:determining a driver action from an instantaneous lateral accelerationproduced from the steering angle, vehicle speed and vehicle constants.31. The method according to claim 29 further comprising: determining asecond lateral acceleration the vehicle is expected to reach when thedriver continues driving into or out of a curve with an almost uniformsteering velocity.
 32. The method according to claim 29 furthercomprising: determining a driver action from lateral acceleration thevehicle is expected to reach, wherein the expected lateral accelerationis produced from the steering angle speed, vehicle speed and vehicleconstants.
 33. The method according to claim 32, wherein the determinedfirst and second lateral accelerations are compared with each other. 34.The method according to claim 32, wherein at least one of determinedfirst and second lateral accelerations is compared with a limit value.35. The method according to claim 26 further comprising: performingbrake interventions on one or more wheel.
 36. The method according toclaim 35, wherein the vehicle speed is reduced by performing the brakeinterventions.
 37. The method according to claim 35, wherein anadditional torque about a vertical axis of the vehicle is forced byperforming the brake interventions depending on actual and nominalrotational data.
 38. The method according to claim 37, wherein theactual rotational data is determined by means by a yaw rate sensor (4)and the nominal rotational data is determined from process variables ina vehicle model.
 39. The method according to claim 37 signals for apressure requirement meant for a braking pressure increase or a brakingpressure decrease in the wheel brakes and producing a determinedadditional torque or a determined speed reduction of the vehicle aregenerated in a driving dynamics control, and corresponding commands areoutput to brake actuators.
 40. The method according to claim 39, thesignals for the brake pressure increase and/or the brake pressurereduction are generated depending on at least one of the variables ofthe lateral accelerations, the vehicle speed, the actual lateralacceleration, or the steering wheel angle.
 41. The method according toclaim 37, wherein the executed intervention is terminated when theexpected critical driving situation or an actual critical drivingsituation are no longer determined.
 42. The method according to claim41, wherein the critical driving situation is no longer determined whenthe variables of the lateral accelerations are below predeterminedthreshold values.
 43. The method according to claim 26, wherein a yawrate is determined which has to be expected due to the driver action.44. The method according to claim 43, wherein the yaw rate to beexpected is compared with a limit value in order to detect a criticaldriving situation.
 45. A system for controlling driving stability of avehicle including sensors (1-5) measuring variables that characterizedriving behavior of the vehicle, the system comprising: a unit (8) forevaluating the measured values of the variables; a device for generatingcontrol signals for controlling at least one of a brake intervention oran engine intervention; a device for determining a driver action fromthe values of the measured variables; a device for determining values ofvariables that characterize a driving dynamics of the vehicle and can bederived from the measured variables and vehicle constants (I, EG),wherein the determined values are values expected in the future due tothe determined driver action; a comparator for comparing the values ofthese variables to be expected with threshold values for thesevariables; and a controller for controlling brake and/or engineinterventions depending on the result of the comparison.
 46. The systemaccording to claim 45, wherein the measured variables are measured foran electronic driving stability control program for the vehicle.
 47. Thesystem according to claim 45, wherein the system includes at least oneof a wheel speed sensor, a steering wheel angle sensor and a steeringangle sensor.
 48. The system according to claim 45, wherein the systemincludes a lateral acceleration sensor.
 49. The system according toclaim 45, wherein the system includes a yaw rate sensor.
 50. The systemaccording to claim 45, wherein the system is provided as component of adriving stability control system in the vehicle.
 51. The systemaccording to claim 50, wherein the driving stability control system isan ABS, TCS, ESP, ARP or similar system
 52. The system according toclaim 45, wherein the system is provided in a the vehicle for preventingrollover of the vehicle.